The present invention relates to an IC card with a solar battery, and, in particular, relates to such a card having a key input, a display, an integrated circuit (IC) for memory and calculation, and, a solar battery as power supply for the above circuits. The present invention is to be used, for instance as a bankbook. The present invention has the feature of containing a solar battery as part of an IC card, but has no secondary battery.
A prior IC card is shown in Japanese patent laid open publication No. 5389/86.
FIG. 10 is a perspective view of the prior IC card in said publication, and FIG. 11 is a circuit diagram of the IC card of FIG. 10. In those figures, on one surface of the card 1, a key input portion 2 having a keyboard for data input, a display device 3 for data display with liquid crystal display element, and a solar battery 4 for power supply, are mounted. And on the other surface of the card contains a terminal 5 for external connection for both data and power supply and an embossment for identification code. A secondary battery 6 coupled with the solar battery 4, and the IC (integrated circuit) 10 are also mounted on the card 1. The IC 10 has a central processing unit (CPU) 11 for calculation, a read only memory (ROM) 12 for storing a program and data, a random access memory (RAM) 13 for storing data, an electrically erasable programmable read only memory (EEPROM) 14 which is a read only memory but is electrically rewritable, a display circuit 15, and a timer-calendar circuit 16. The EEPROM 14 is a read only memory, but is rewritable by applying a predetermined voltage, and maintains contents with no power supply. The EEPROM 14 includes a voltage booster for raising the voltage to operational voltage of the EEPROM (for instance, 21 volts), to rewrite data, a first storage area for storing a secret number and/or an identification number, and a second storage area for storing the count number of incoincidence between said secret number and the number which is input by the card owner.
In operation, when the IC card is used for payment, the display is first cleared by operation of the key input 2, then, the secret code is input to the CPU 11 through the operation of the key input 2. Then, the CPU 11 compares the secret code stored in the EEPROM 14 with the input data from the key input 2, and if they are coincident with each other, the code "OK" is displayed on the display unit 3 through the display circuit 15. Thus, it is confirmed that the user is the true card owner, and so, the store clerk processes the IC card with an emboss-in-printer, similar to a conventional credit card.
On the other hand, if the code from the key input 2 differs from the content of the EEPROM 14, the CPU 11 displays the fact of the incoincidence on the display unit 3, and urges the re-try. The CPU 11 counts the number of the incoincidence by using the second storage area in the EEPROM 14 by storing the count number of the incoincidence in that area. When the content of that second area reaches "5", the CPU 11 recognizes that the user is not the true card owner, makes the card invalid, and displays that the card is invalid on the display unit 3. Therefore, the illegal use of an IC card is prevented.
The power supply to the IC 10 is effected by the secondary battery 6 which is charged by the solar battery 4. Therefore, even when the solar battery does not operate in dark circumstance, the IC 10 has power supplied, and so, the IC 10 can operate even in insufficient light.
As for a solar battery, the ELA015 (trade name) described in "Fuji amorphous silicon solar battery" manufactured by Fuji denki Co. Ltd, is commercially obtainable in the market. The external size of that solar battery is 35.1.times.13.7.times.0.1 (mm), and the electrical characteristics are that the output voltage is 1.5 V and the operational current is 6 .mu.A in 200 Lux. That solar battery has a single plane layer of four amorphous silicon elements connected in series to one another.
However, a prior IC card with a prior solar battery has disadvantages as follows.
In said Japanese patent laid open publication 5839/86, no description is given for the power consumption in the IC 10, the output power of the solar battery 4, and the capacity of the secondary battery 6. In our analysis, a prior solar battery having a single layer structure cannot operate an IC card, which updates the contents of the EEPROM 14 according to the number of errors of the input of the identification number, if it is assumed that no external power supply is used, and that the size of an IC card is a standard one (86.times.54 mm.sup.2). An EEPROM 14 requires the power consumption of 1.35 V, 20 .mu.A only for writing several bits of data, and the necessary power consumption of the EEPROM 14 increases as the number of bits increases. In other words, a prior single layer solar battery can not operate an IC card which updates an EEPROM.
The size of an IC card is standardized internationally to 86.times.54 mm.sup.2, which has the area of 4644 mm.sup.2. And, the area for the solar battery is for instance 924 mm.sup.2 (20% of the whole area of an IC card), which is the rest of the area of the IC card which mounts other members.
When the area for a solar battery is fixed to 924 mm.sup.2, the characteristics of a prior single layer solar battery is analyzed below.
A prior single layer solar battery 50 in FIG. 12 has a substrate 51 made of stainless steel of the width 0.05-2 mm, an insulation layer 52 made of polyimide resin deposited on the substrate 51, and the conversion cells 53-1 through 53-3 deposited on the insulation layer 52. Those cells are deposited on one plane and are connected in series to one another. Each of the cells 53-1 through 53-3 is produced through plasma CVD process, having a conductive metal electrode 53a, a single layer of opto-electric conversion layer 53b made of P-I-N (or N-I-P) type amorphous silicon, and a transparent electrode 53c. A dead space 54 is provided to separate each cells 53-1 through 53-3. The three cells are connected in series by connecting the electrode 53c of the first cell 53-1 to the electrode 53a of the second cell 53-2, and connecting the electrode 53c of the second cell 53-2 to the electrode 53a of the third cell 53-3.
FIG. 13 shows the curves between voltage and current of the solar battery 50 in FIG. 12, in which the horizontal axis shows the output voltage V (volts), the vertical axis shows the output current (.mu.A), and the light intensity is 200 Lux (fluorescent lamp). In FIG. 13, the curve 60 shows the characteristics when four cells are connected in series, the curve 61 shows the case of three cells connected in series, and the curve 62 shows the case of two cells connected in series. The shadowed area A shows the area that the write operation to the EEPROM 14 in the IC 10 is possible. The write operation to EEPROM 14 needs the voltage about 1.35 V, and the current higher than 20 .mu.A.
It should be noted in FIG. 13 that none of the curves 60, 61 and 62 crosses with the area A. It means that a prior single layer solar battery of FIG. 12 can not operate the EEPROM 14 in the IC 10. Although the IC 10 might operate with a prior single layer solar battery if the light intensity would be very high, it is not practical.
If we try to update an EEPROM in a prior IC card, we must use a large solar battery so that higher power is obtained, or a large secondary battery must be used. However, since the size and the depth of an IC card are given, if the size of a solar battery mounted in the IC card is large, the area for other components must be decreased. Thus, the area for a key input 2 and/or display unit 3 would be decreased, and so, the operation of a key input 2 would become inconvenient, and/or the number of characters on the display unit would be decreased, or at least the size of the characters on the display unit would be decreased. Similarly, if we try to use a large secondary battery, the area for other components must be decreased, and/or the size of an IC card itself must be increased.